Drawing, that is the reduction of the section of a wire or other metal article through threading dies, is obtained by pulling the material through the threading die by means of drawbench machines.
A commonly used technique specially for metal wires with round section enables the drawing of metal wire to be obtained by means of successive section reductions due to the wire passing through threading dies positioned one after the other and contained, together with a tank containing lubricant for the wire, in a single equipment for wiredrawing. Lubrication in this equipment is achieved by means of interposition of lubricant between the metal wire and the threading die because of both the motion of the wire towards the threading die and the spatial geometric profile of the threading die itself.
Apparatus that enables optimal lubrication to be achieved during the entire cold-drawing operation has been described in the Italian Patent No. 1230396. This apparatus comprises an external body internally fitted with a tank containing a lubrication material. Said tank has at one end an input hole for a metal wire to be drawn, and is fitted at the other end with a first sleeve fitted with a cylindrical hole whose diameter exceeds that of the wire and a threading die fitted with a truncated cone hole with decreasing diameter towards the output so as to enable the reduction of the diameter of the wire. A spacing element of suitable conformation is positioned between the threading die and the sleeve for joining the output holes from the sleeve and the input holes into the threading die and which acts as gasket for the equipment's cooling water.
Another apparatus for cold drawing of a metal wire is described in the Italian Patent application No. MI99U000587 dated 24 Sep. 1999. The apparatus is similar to the previously described apparatus except for the fact that it does not comprise the spacing element between the sleeve with cylindrical hole and the threading die with conical hole. The sleeve terminates with an extension inserted into the conical hole of the threading die so that it is impermeable to the apparatus cooling water. Both the sleeve and the threading die are held in position by means of a threaded plug fixed to a support which in turn is fixed by means of screws onto the external body of the apparatus.
Nevertheless, mounting the threading die onto the sleeve can become a complicated operation; in fact this operation sometimes has to be repeated various times because it is difficult to insert the threading die onto the sleeve with simultaneous fastening of the threaded plug onto the body.